A closed circuit consists of n cells connected in series. Each cell has an emf e and internal resistance r. The resistance of the connecting wires is assumed to be zero. What will be the reading of voltmeter connected to the terminals of one of the cells? It is assumed that the voltmeter has an infinitely high resistance as usual. Can it be real in practice?

Explanation

In the referred circuit no additional resistance is connected and the resistance of the connecting wires is also zero [Fig.1.45] i.e the two terminals of the combination of the cells have been shorted circuited.
In this case the current through the circuit (`because R=0`)
`I=(n e)/(nr)=e/r`
So the potential difference of the two ends of any cell is
`V=e-Ir=e-e/r.r=e-e=0`
So the reading of the voltmeter connected to the terminals of the cell is zero.
In practice, this is not possible. (1) For all practical purposes the resistance of the connecting wires are not zero (2) the resistance of the voltmeter used are not infinite.It is connected in parallel with the internal resistance r of the cell. So the equivalent resistance of the combination becomes less than r. Hence, the reading of the voltmeter is not exactly zero.